vig/src/parser.zig

const std = @import("std");
const scanners = @import("scanner.zig");
const main = @import("main.zig");
const ast = @import("ast.zig");
const tokens = @import("tokens.zig");
const err = @import("errors.zig");

const Allocator = std.mem.Allocator;
const Scanner = scanners.Scanner;
const Token = tokens.Token;
const TokenType = tokens.TokenType;
const Result = main.Result;
const Node = ast.Node;

pub const Parser = struct {
    allocator: *Allocator,
    scanner: *Scanner,

    tokens: []Token = undefined,

    pub fn init(allocator: *Allocator, scanner: *Scanner) Parser {
        return Parser{ .allocator = allocator, .scanner = scanner };
    }

    fn doError(self: *Parser, comptime fmt: []const u8, args: ...) Result!void {
        std.debug.warn("parser error at line {}\n\t", self.scanner.line);
        std.debug.warn(fmt, args);
        std.debug.warn("\n");

        return Result.CompileError;
    }

    fn peek(self: *Parser) Token {
        return self.tokens[self.tokens.len - 1];
    }

    fn previous(self: *Parser) Token {
        return self.tokens[self.tokens.len - 2];
    }

    fn tokenError(self: *Parser, token: Token, msg: []const u8) Result!void {
        if (token.ttype == .EOF) {
            err.report(token.line, " at end", msg);
        } else {
            err.reportFmt(token.line, " at '{}': {}", token.lexeme, msg);
        }

        return Result.CompileError;
    }

    fn isAtEnd(self: *Parser) bool {
        return self.peek().ttype == .EOF;
    }

    fn check(self: *Parser, ttype: TokenType) bool {
        if (self.isAtEnd()) return false;
        return self.peek().ttype == ttype;
    }

    fn nextToken(self: *Parser) !Token {
        var token: Token = undefined;

        while (true) {
            var next_token_opt = try self.scanner.nextToken();
            if (next_token_opt) |token_nice| {
                token = token_nice;
                break;
            }
        }

        self.tokens = try self.allocator.realloc(
            self.tokens,
            self.tokens.len + 1,
        );

        self.tokens[self.tokens.len - 1] = token;
        return token;
    }

    fn consume(self: *Parser, ttype: TokenType, comptime msg: []const u8) !Token {
        if (self.check(ttype)) return try self.nextToken();

        try self.tokenError(self.peek(), msg);
        return Result.CompileError;
    }

    fn consumeSingle(self: *Parser, ttype: TokenType) !Token {
        std.debug.warn("consume {}, has {}\n", ttype, self.peek().ttype);

        if (self.check(ttype)) {
            var cur = self.peek();
            _ = try self.nextToken();
            std.debug.warn("now has {}\n", self.peek());
            return cur;
        }

        var buf_main: [1000]u8 = undefined;
        var buf = try std.fmt.bufPrint(
            buf_main[0..],
            "expected {}, got {}",
            ttype,
            self.peek().ttype,
        );
        try self.tokenError(self.peek(), buf);

        return Result.CompileError;
    }

    fn mkFnDecl(self: *Parser, name: Token, params: ast.ParamList) !*ast.Node {
        var node = try self.allocator.create(Node);
        node.* = Node{
            .FnDecl = ast.FnDecl{
                .func_name = name,
                .params = params,

                // TODO replace by arg when statements work
                .body = ast.NodeList.init(self.allocator),
            },
        };
        return node;
    }

    fn functionDecl(self: *Parser) !*ast.Node {
        _ = try self.consumeSingle(.Fn);
        var name = try self.consumeSingle(.Identifier);
        _ = try self.consumeSingle(.LeftParen);

        var param_list = ast.ParamList.init(self.allocator);

        while (true) {
            var tok = self.peek();

            switch (tok.ttype) {
                .RightParen => break,
                .Identifier => {},
                else => try self.doError("expected identifier, got {}", tok.ttype),
            }

            var typetok = try self.nextToken();
            if (typetok.ttype != .Identifier) {
                try self.doError("expected identifier for type, got {}", typetok.ttype);
            }

            var param = try self.allocator.create(ast.ParamDecl);
            param.* = ast.ParamDecl{ .param_name = tok, .param_type = typetok };

            std.debug.warn("param! {}\n", param);
            try param_list.append(param);
            tok = try self.nextToken();
        }

        // function body
        _ = try self.nextToken();
        _ = try self.consumeSingle(.LeftBrace);
        while (true) {
            var tok = self.peek();
            if (tok.ttype == .RightBrace) break;
            // TODO statements?
            //var node = self.processToken(tok);
        }

        _ = try self.consumeSingle(.RightBrace);

        return try self.mkFnDecl(name, param_list);
    }

    fn processToken(self: *Parser, token: Token) !*ast.Node {
        var node = switch (token.ttype) {
            .Fn => try self.functionDecl(),
            else => blk: {
                try self.doError("TODO handle {}\n", token.ttype);
                return Result.CompileError;
            },
        };

        return node;
    }

    pub fn parse(self: *Parser) !*ast.Node {
        self.tokens = try self.allocator.alloc(Token, 0);
        var root = try ast.mkRoot(self.allocator);

        while (true) {
            var token = try self.nextToken();

            if (token.ttype == .EOF) break;

            var node = try self.processToken(token);
            std.debug.warn("node: {}\n", node.*);
            try root.Root.append(node);
        }

        return root;
    }
};